Gas analyzer



J. HlLLlER GAS ANALYZER ApriI' 26, I949.

Filed Aug. 7, 19-47 coxv eoz. CIRCUIT REGULATED CURkf/VT SUPPLY R M/ m K a R 6 7 M w P M VACUUM v INVENTOEQ. limes Mew ATTORNEY J. HILLIER GA$ ANALYZER April 26,1949.

2 Sheeis-Sheet 2 Filed Aug. '7, 1947 w w 5 47 "m of l MV 7 w .t v a W m E 65 H 1 w INVENTCBR. James [Z1110]- ATTORNEY Patented Apr. 26, 1949 GAS ANALYZER James Hillier, Cranbury, N. J., assignor toRad io Corporation of America, a corporation of Delaware Application August 7, 1947, Serial No. 767,262"

19 Claims. (Cl; 250-495) This invention relates generally to electron or electrical deflecting field which deflects the transmitted electrons as a function of their velocities. The deflected electrons are passed through a slitand strike-a collectin electrode of an electron multiplier. In general, the apparatus for accomplishing this comprises a monokinetic electron source, means for controlling a stream of electrons derived from the source, means for irradiating a, gaseous specimen with the controlled electron stream and high resolving power means for analyzing the velocity distribution resulting from the inelastic collisions of the electrons with the atoms of the gas.

Previously, analyzers, ,such as that described in PatentNo. 2,418,228'1of the instant inventor, have been designed 'for the electron analysis of solids which either transmit or reflect electrons. This samegeneral type of apparatus has been modified for gas. analysis by. making. certain changes among which are .the addition. of a novel capsule for holding the gaseous. specimenin the electron beam while allowing passage of the electrons, and a different improved system. for. de-

tecting and measuring the residual energy of the electrons.

One object of the present inventionis to provide an electronic analyzerior .the study of gaseous specimens.

Another object of the inventionis to provide an improved apparatus, for analyzing minute specimens of a gas.

Another object of theinvention is to provide an electronic apparatus for the. analysisof'a gas wherein a permanent record ofthe analysis is made automatically.

Another object, of the invention is to provide an improved electronicapparatus for gas analysis inwhich the gas being analyzed has almost no streaming motion Anotherobject of-the' invention is toproyide image of the source.

2 an improved means'for subjecting a'minute area of a gaseous material to electron irradiation, subjecting electrons transmitted by said material to a uniform'magnetic field, and indicating the relative velocities of electrons subjected to said magnetic field;

Still'another object of the invention is to provide an improved methodfordetermining fundamental information about thestructure' of gaseous molecules. v

These and otherobjects will be more apparent and the invention will be better understood from a' study ofthe specification, including the accompanyin drawings in'which like parts are incheated by similar reference numerals;

Fig. l is a diagrammaticview' of apparatus embodying the present invention,

Fig. 2 is a longitudinal 'crosssection view of the apparatus of Fig. 3 taken along the line 2-2.

Fig. 3 is'anenlarged plan view of part of the apparatus shown in Fig. 1, I

Fig. 4 is a diagrammatic view of a modification of theapparatus showifin 1, and

Fig. 5 is a longitudinal cross section view of the apparatus of Fig.'3 taken along the'line 5-5.

Fig. 6 is a fragmentary section through line 66 of Fig. 2.

Referring nowto 1, part of the analyzing system is enclosed in a continuously pumped vacuum chamber 2 which'is not demountable and is preferably made of glass, in orderthat it can be thoroughly outgassed and the-highest possible vacuum obtained. The degree of vacuum should be that of a goodelect'ron microscope or around 10 to 10- of mercury. Within this chamber is mounted an electron optical system. comprising an electron source made up of a hairpin tungsten filament '4, which issurrounded by a focusing aperture 6. The filament is connected to a source 8 of high voltage and is preferably maintained at a negative potentialof the order of 2,000 volts, although itmay-be used at potentials of as low as two hundred volts.

The stream of. electrons-emanating from the electron source is-passed through two reducing lenses Ill and I2 which form a reatly reduced Although these lenses are shown as being of the conventional electrostatic form, they may also be the usual type'of electromagnetic lenses.

One of the improvements of the present invention is constituted'bythenovel form of apparatus for introducing the gas" to be analyzed into'the electron optical system. I This apparatus consists,

1 in general, of an inlet pipe l4lconnected to a source of the gas (not shown), a valve It for regulating the amount of gas flowing into the vacuum system, and a capsule it for containing the gas in the path of the electron beam.

In order not to impose an undue burden on the vacuum pumps, the gas is introduced into the capsule at very low pressures. Although this pressure is not critical, it is preferably of the order of 1 mm. of mercury. The exact pressure will depend mainly on the size of the restricting apertures through which the gas escapes into the vacuum chamber and which at the same time permit passage of an electron beam through the sample.

The capsule i8 which is shown in more detail in Figs. 2 and 5 comprises, in general, a gas chamber for containing the as sample to be analyzed and means for introducing a small quantity of the gas into the path of the electron beam at a desired location. The several parts of the capsule have been made movable with respect to each other in order to provide for the accurate positioning necessary in an electron optical system.

Referring now to Figs. 2 and 5, the capsule 18 comprises three principal members, parts of which are concentrically arranged. The innermost member l9 and the intermediate member 20 cooperate to provide a gas chamber 2! of annular cylindrical form. The outermost member 22 serves as a supporting base for the other two parts l9 and 20 and permits the accurate positioning of these parts with respect to each other in a manner which will be described later. The innermost member I!) consists of three parts. A vertically extending cylindrical portion 23 of the member 19 has a cylindrical central passage 24 which provides a path for the electron beam while the outer walls of this portion 23 constitute the inner walls of the gas chamber 2!. The member l9 also has a horizontal flanged portion 25 which provides one end for thegas chamber 2! and a cap 26 fitting over the free end of the cylindrical portion 23, which cap has a small aperture 2'! for permitting passage of electrons.

Forming a part of intermediate capsule member 20 is a vertically extending cylindrical wall portion 28, the inner wall surface of which constitutes the outer wall of gas chamber 2i. The member 20 is also provided with a thickened shoulder portion 29 and a horizontally extending end plate 30 across the lower end of the member. The end plate 30 has a, narrow aperture 3! therein through which the electron beam passes. The cap 26 and end plate 30 are positioned in opposed relationship to each other and are spaced a, very small distance apart; i. e., of the order of 0.001 to 0.005 inch. They thus cooperate to form a very narrow passage 32 connecting with the 1 gas chamber 2| in which there is always present a small volume of gas which has difiused in from the larger chamber. The apertures 21 and 3| opening into the passage 32 provide the means of permitting the electron beam to traverse a small portion of the gas being analyzed. The passage 32 and the apertures 21 and iii are so restricted in width that the volume of gas which escapes into the vacuum chamber 2 is quite small and can easily be handled by the pumps.

The outer member 22 of the capsule I8 has a circular end plate 33 fitting slidably against the lower end of wall portion 28, this end plate having a cylindrical passage 34 therein which serves as a continuation of the passage 24.

As mentioned previously, it is important to the successful operation of the apparatus that the apertures 27 and SI be accurately aligned with respect to each other. It is also important that both apertures be positioned properly in the path of the electron beam. For this reason, the three principal parts I9, 20 and =22 of capsule l8 are so made as to be adjustably positioned with respect to each other and are capable of having very fine adjustments made in their relative positions. The lower surface of flanged portion 25, the up per and lower surfaces of shoulder portion 29, the upper surfaces of outer member 22 and other minor parts which slidably engage should be accurately machined to permit sliding adjustment while some of them must at the same time be gas tight to prevent escape of abnormal amounts of gas into the vacuum chamber 2 from gas chamber 2i.

As best. illustrated in Figs. 3 and 5, the inner member l9 and the aperture 2'1 associated therewith may be positioned by adjusting four set screws 35 threaded through shoulder portion 29 of intermediate member 2%. The intermediate member '29 and aperture 3| associated therewith may be positioned by adjusting four other set screws 35 threaded through Wall portion 31 of outer member 22. When the positioning has been accomplished, bolts 39, the shanks of which pass through all three members i9, 20 and 22, are tightened to hold the parts firmly in their adjusted positions. Only the bolt passages through member 22 are threaded since the passages through members !9 and 20 must be left somewhat larger than the shanks of the bolts 39 in order to allow a sufiicient degree of freedom in acljustably positioning these members.

The reducing lenses l0 and i2 form a greatly reduced image of the electron source between the apertures 2'l and 31 where the gas is introduced to the path of the streaming electrons. The electrons undergo inelastic collisions with gas molecules and those which have collided lose a quantity of their original energy, which quantity depends upon the nature of the gas being analyzed.

The electrons which have passed through the gas then pass through another reducing lens 38, which focuses an image of the electron source at the edge of a homogeneous field magnetic analyzer of the type. This analyzer is made up of one or more field coils 40 which are placed adjacent a U-shaped portion 42 of the vacuum chamber '2, a, regulated current supply l to supply current to the field coil M! and a control circuit ed for varying the strength of the field in a desired manner. Preferably, two field coils 40 are used, one being placed on either side of the U-shaped portion 42 of the vacuum chamber. The current supply and control circuit may be any one of many well known conventional types, one example being that illustrated in Fig. 7-9, page 237, of Electron Optics and the Electron Microscope by Zworykin et al., New York, John Wiley and Sons, Inc., 1945.

The magnetic field generated by the field coil causes the electrons to traverse substantially semicircular paths through the field, whereupon, the electrons strike a plate 8 adjacent one end of the U-shaped tube portion 62 in which there is a collecting slit 50. The magnetic field generated by the field coil 40 will deflect the electrons different amounts determined by their respective residual energies or velocities, whereby an energy distribution pattern will be formed at the plate 48. The focus of the pattern is controlled by; adjusting the pbtentis1 =tn-the "third lens 38'. BY'reguIati'n'g the strength or the mag pattern of-the'transmi-tted enetron caebeswept 1 or scannedacross the slit fifli The-electrons passing through the slit fromany'se-lected part f thepattel'n' Strikea collebtingeiectl'ode526f preferably-used'is a standard commercial sustemultiplier with" the bhdtosensiti'v e eateries-cremoved.

It should be understood that the el't'ron opti- 'cal lens system takes no part in-the actual aha-lysis of the gas specimen but is introduced only asf'a means of increasing the resolving power (if the magnetic analyzer. The first two lenses 1 [I and l2"prc' duce such a smallsourcethat'wherr'it is imaged at" the slit" posti-on of themagneue fildt-'5 of the analyzer, it is too small to influence 'the resolving power of the analyzer. 38 of the system. can beprovided with apertures which, themselves; provide a means of controlling the resolving power of the analyzer. 1

It should be further understood that the deflecting field may be electrostatic instead of electromagnetic', or it may be a combination of electrostatic and electromagnetic. The use Of. an

electrostatic deflecting. :field in: l the analyzer. is

illustrate'd'in Fig. 4. Electrodes 1'60 and1li2i ofeopposit polarityare placed adia'c'ent thett'curved walls of the deflection chamber lz. These electrodes are connected to the variable high potential source 8. The electrons are deflected by the electrostatic field set up and are caused to travel in semi-circular paths. The paths of the electrons with the greatest residual velocity or energy are bent the least while those with lesser residual energy are deflected to a greater extent. In this way, a distribution pattern is set up as when an electromagnetic field is used. The pattern may be swept across the slit 50 by varying the field strength.

It is not necessary that the electromagnetic or electrostatic field be set up such that an average deflection of 180 is obtained. Any other angle of bending may be used depending upon convenience. Shape of the electrodes and strength of the field will determine the angle of deflection obtained.

The above described method of analyzing a gas may be used to provide several types of fundamental information. From an interpretation of the electronic energy distribution pattern, a measure is provided of two things:

(1) A spectrum of the possible energy losses which an electron can suffer in an inelastic collision with a gas molecule,

(2) The relative probability of occurrence of such collision.

The energy loss can be interpreted in a number of ways, depending upon its magnitude. Most important is the energy connected with the breaking of bonds in the molecule. For example, in many organic compounds which can exist in gas or vapor form, each molecule contains many carbon to carbon linkages which may be either single, double or triple. Many other types of bonds may also be present. Every time one of The third lens masseuse-is ewesmwampaa or electron, the electron loses energy. Th's--- energy losses will appar as'a seriesbf lines in the energy distribution spectrumw Thus, a valuable tool is pro- ?videdior the'stud'y or the fundamental structure of meieemesas wel-l a's-for the accurate identiflcation of-a', large number of organic and inorganic compounds? From a study of the-patterns obtainedfrom-known molecules; it is also possible 'trijl.edi icetl'ie' structure of unknown molecules;

There has thus been described an improved meansand method --for obtaining information concerning-the basicmolecular structure of substances in i gaseousor vapor form. Although cer- *t'ain preferred embodimentsof apparatus used in performing the invention have been described, othermodiflcationswi-ll be obvious to those skilled in"tlie"art'an-dit is desired that the invention be limited only by the appended claims.

I cl aint as'my invention 1. Inan apparatus for'analyzinga gaseous ina- .terial, means for subjecting a sample of said matens-1 "to j a beam of electrons, means for producmg an. electrical field for deflecting the paths-of electrons transmitted" through saidmaterial and means .for detecting the residual energy in said transmittedelectrons.

v 2. In an apparatus foranalyzinga gaseous ma.- terial, an electron. optical systemfor focusing a beam of electrons at a predetermined point,

means for admitting gaseous material into the path of said beam of. electrons .at said point; electrical means ror deflecting the pathsof electrons transmitted through said material and means for iaeteeurlg the residual energy in said transmitted electrons.

3. xmanapparatus for; analyzing a gaseous mat'ei'ial, a vacuum chamber and means for continuously evacuating the same, means for providing a beam of electrons within said vacuum chamber, means for introducing a small quantity of a gaseous material at low velocity into the path of said beam without appreciable lowering of the vacuum within said chamber, electrical means for deflecting the paths of electrons transmitted through said material, and means for detecting the residual energy in said transmitted electrons.

4. In an apparatus for analyzing a gaseous material, a vacuum chamber, means for producing a beam of electrons within said vacuum chamber, a gas chamber for said gaseous material mounted within said vacuum chamber and having apertures therein positioned in the path of said electron beam, means for deflecting the paths of electrons transmitted through said gaseous material and means for detecting the residual energy in said transmitted electrons.

5. In the apparatus of claim 4, an electron optical system for focusing said beam of electrons.

6. In the apparatus of claim 4, means for adjusting the position of said apertures.

7. In the apparatus of claim 4, means for varying the strength of said deflecting means an an eletron multiplier tube having a collecting electrode positioned in the path of the electrons deflected by said deflecting means.

8. The apparatus of claim 4 in which said deflecting means is adapted to deflect said transmitted electrons in a substantially semicircular path.

9. The apparatus of claim 4 in which said deflecting means includes means for producing an electromagnetic field.

10. The apparatus of claim 4 in which said de- 7 fleeting means includes means for producing an electrostatic field.

11. In an apparatus for analyzing a gaseous material, a vacuum chamber, means for continuously evacuating said vacuum chamber, means for producing a beam of electrons within said vacuum chamber, a gas chamber for said gaseous material mounted within said vacuum chamber and having apertures therein adapted to allow passage of electrons in said beam through said gas, means for admitting gas into said gas chamber from a source outside said vacuum chamber, magnetic means for deflecting the paths of electrons transmitted through said gaseous material and means for detecting the residual energy in said transmitted electrons.

12. In the apparatus of claim 11, means for amplifying the energy detected by said detecting means.

13. In the apparatus of claim 11, means for indicating the quantity of energy detected by said detecting means.

14. A method of analyzing a gaseous material comprising subjecting said material to a beam of electrons within a vacuum, deflecting electrons transmitted through said gas by means of an electrical field and detecting the residual energy of said electrons.

15. A method according to claim 14 which includes measuring and recording the amounts of residual electron energy after detecting the same.

16. In an apparatus for analyzing a gaseous material, means for subjecting a sample of said material to a beam of electrons, means for producing an electrical field for deflecting the paths of electrons transmitted through said materialin proportion to their residual energies whereby a distribution pattern of deflected paths is obtained of said energies, a slit positioned in the path of the deflected electrons but narrower than the width of said distribution pattern, means positioned behind said slit for detecting the residual energies in said deflected electrons and means for scanning said deflected paths across said slit.

17. Apparatus according to claim 16 including means for recording the amounts of energy detected by said detecting means.

18. In an apparatus for electronically analyzing a sample of material including means for generating a beam of electrons, means for introducing said sample in the path of said beam, means for deflecting the paths of electrons transmitted through said sample and means for detecting the residual energy in said transmitted electrons, the improvement comprising means for introducing a gaseous sample in the path of said beam.

19. Apparatus according to claim 18 in which said means for introducing a gaseous sample is a gas chamber having apertures communicating with the supply of gas within said chamber, said apertures being positioned in the path of said electron beam whereby said beam is permitted to be transmitted through a portion of said sample.

JAMES HILLIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,405,306 Hillier et al. (A) Aug. 6, 1946 2,408,487 Smith Oct. 1, 1946 2,418,228 Hillier (B) Apr. 1, 1947 

